Abstract
The mechanisms underlying age-related differences in maximum power production during multi-joint exercises are not fully understood. One factor that could contribute to these age-related differences is a differential development of the ability to generate maximum strength and power across the involved joints. Therefore, the purpose of this study was to investigate the age-related changes in knee extensor and plantarflexor strength under isometric and isokinetic conditions. Ten boys (11.6 ± 0.8 yrs) and 10∼male adults (27.7 ± 5 yrs) participated in the study. Ankle plantarflexion and knee extension strength were measured isometrically and isokinetically at 30, 75 and 120°/s. Muscle activity (EMG) from the Gastrocnemius Medialis and Vastus Lateralis was also recorded. Multivariate analyses of variance identified significant Age by Joint interactions for isometric peak torque (PT) and isokinetic peak joint powers for all conditions (p<0.05). Effect sizes revealed that under isometric conditions, the difference between peak plantarflexor and knee extensor torques was moderate in children, whilst in adults, this effect was large. Under isokinetic conditions, the effect sizes describing the differences between peak joint powers produced at the ankle and knee joints were large for both children and adults. A MANOVA revealed that the Age by Muscle interaction for the magnitude of muscle activity was non-significant (p> 0.05). Our results suggest that the development of lower limb isometric strength is joint-dependent and that this joint dependence is not due to a muscle-specific development of motor unit recruitment.